A better use for $700 B

$700B for a war? In hindsight, we should have bought cars...

A Prius in Every Garage: Bob's $700 billion Christmas wish list

The biggest hand-waving statement of Bob's is to give them to the "biggest users", but that would probably be difficult to determine. I would alternatively use the vehicle it would be replacing as a guide; start with the older and larger vehicles. This would have the nice side effect of helping out more folks who couldn't otherwise afford a new vehicle and may have trouble maintaining the one they have.